1. Field of the Invention
This invention relates to a data transfer control device and electronic equipment comprising the same.
2. Description of Related Art
An interface standard called IEEE 1394 has recently been attracting much attention. This IEEE 1394 has standardized high-speed serial bus interfaces that can handle the next generation of multimedia devices. IEEE 1394 makes it possible to handle data that is required to have real-time capabilities, such as moving images. A bus in accordance with IEEE 1394 can be connected not only to peripheral equipment for computers, such as printers, scanners, CD-R drives, and hard disk drives, but also to domestic appliances such as video cameras, VTRs, and TVs. This standard is therefore expected to enable a dramatic acceleration of the digitalization of electronic equipment.
The concept of IEEE 1394 is disclosed in various publications, such as xe2x80x9cAn outline of the IEEE 1394 High Performance Serial Busxe2x80x9d (Interface, April 1996, pages 1 to 10), xe2x80x9cBus Standards for PC Peripheral Equipmentxe2x80x9d (Interface, January 1997, pages 106 to 116), and xe2x80x9cReal-Time Transfer Modes and Multimedia-Capable Protocols for IEEE 1394-1995 (FireWire)xe2x80x9d (Interface, January 1997, pages 136 to 146). Texas Instruments"" TSB12LV31 is known as a data transfer control device that conforms to IEEE 1394.
However, some technical problems have been identified with such a data transfer control device conforming to IEEE 1394, as described below.
That is to say, the current IEEE 1394 standard does make it possible to implement transfer speeds up to a maximum of 400 Mbps. In practice, however, the presence of processing overheads forces the actual transfer speeds of an entire system to be much slower. In other words, the firmware and application software running on a CPU require large amounts of time for processes such as preparing for transmitting data and reading in received data, which means it is not possible to implement high-speed data transfer overall, no matter how fast the data can be transferred over the IEEE 1394 bus.
A particular problem lies in the fact that a CPU incorporated into peripheral equipment has a lower processing capability than the CPU incorporated into the host system, such as a personal computer. This makes the problem of processing overheads in the firmware and application software extremely serious. It is therefore desirable to provide techniques that are capable of efficiently solving this overhead problem.
This invention was devised in the light of the above described technical problem, and has as an objective thereof the provision of a data transfer control device and electronic equipment using the same which are capable of reducing the processing overheads of firmware and application software, thus implementing high-speed data transfer within a compact hardware.
In order to solve the above described technical problem, there is provided a data transfer control device for transferring data among a plurality of nodes that are connected to a bus, according to a first aspect of the present invention. This data transfer control device comprises: a circuit for diagnosing a self identification packet and for automatically detecting a node that is qualified to become a manager having a given management function based on the results of the diagnosis, when the self identification packet containing basic information on each node is transferred from each node; and first holding means for acquiring the identification number of a detected node from basic information in the self identification packet sent by that node, and for holding that identification number.
This aspect of the invention ensures that the identification number of the node that is qualified to become the given manager is detected automatically by the hardware, and this identification number is held in the first holding means configuration of a register or semiconductor memory, by way of example. This arrangement makes it possible to reduce the processing load on the firmware or the like that is controlling data transfer. This also makes it possible to expect improvements in actual transfer speeds and reductions in the costs of devices.
An identification number of a node may be overwritten onto an identification number previously held in the first holding means, when it is determined from basic information in the self identification packet sent by the node that the node is qualified to become the manager having the management function, on condition that self identification packets are sent in sequence starting from nodes furthermost from a root node within node connection topology. This arrangement makes it possible to detect the node that is qualified to become the manager in a simpler manner, by skillfully utilizing a sequence in which the self identification packets are sent in.
The data transfer control device may further comprise a circuit for detecting whether or not the system is within a self identification period, based on status information sent in from a lower layer; and a packet that arrives within the self identification period may be assumed to be a self identification packet, and a node that is qualified to become the manager may be automatically detected based on that self identification packet. This configuration makes it possible to detect whether or not a packet that is to be processed is a self identification packet, in a simple manner, which makes the hardware more compact.
The data transfer control device may further comprise second holding means for holding information indicating that the self-node is the manager having the management function, when the identification number of a node that is qualified to become the manager matches the identification number of the self-node. This arrangement makes it possible to know whether or not the self-node is the manager having the management function, in a simple manner.
In this data transfer control device, a judgement may be made as to whether or not the identification number of a node that is qualified to become the manager matches the identification number of the self-node, using both a first signal that becomes active on condition that the identification number of the self-node has become definite and a second signal that becomes active on condition that a self identification period has ended. Use of the first signal ensures that correct action is taken even if the identification number of the self-node becomes definite after the self identification period has ended. Use of the second signal ensures that correct action is taken even if the node that is qualified to become the manager is changed after the identification number of the self-node has become definite.
In this data transfer control device, a judgement may be made as to whether or not the identification number of a node that is qualified to become the manager matches the identification number of the self-node, using a third signal that becomes active on condition of the detection of a subaction gap. This arrangement makes it possible to correctly detect a match between the identification number of a node that is qualified to become the manager and the identification number of the self-node, with a simple circuit configuration when the setup incorporates physical-layer devices wherein the identification number of the self-node always becomes definite within the self identification period.
This data transfer control device may further comprise means for reading out from the first holding means the identification number of a node that is qualified to become the manager and for controlling data transfer by use of the read-out identification number. Firmware running on a central processing unit can be considered as an example of this data transfer control means.
Note that the manager having the management function in accordance with this invention is preferably an isochronous resource manager conforming to the IEEE 1394 standard.
According to a second aspect of the present invention, there is provided electronic equipment comprising: any one of the above described data transfer control devices; a device for performing given processing on data that has been received from another node via the data transfer control device and the bus; and a device for outputting a storing data that has been subjected to the processing. According to a third aspect of the present invention, there is provided electronic equipment comprising: any one of the above described data transfer control devices; a device for performing given processing on data that is to be sent to another node via the data transfer control device and the bus; and a device for taking in data to be subjected to the processing.
These aspects of the invention make it possible to increase the speed of processing in the electronic equipment for outputting or storing data that has been transferred from another node, or processing in the electronic equipment for transferring data that has been taken in to another node. These aspects of the invention reduce the processing load on firmware or the like that controls data transfer, thus making it possible to reduce the costs and size of the electronic equipment.